An optical computer mouse typically includes an optical navigation sensor apparatus, having a number of separate components, including an electronic chip that functions as a miniature digital camera to continually record images of a surface that the mouse is resting upon, and determine the speed and direction that the mouse is being moved across the surface by comparing sequentially recorded images of the surface. The images are recorded at a very high rate, such as 1500 images per second, and the resolution of the sensor is high, so that very small movements of the mouse can be detected.
The optical navigation sensor apparatus typically includes a light source, in the form of a light emitting diode (LED), for illuminating a small area of the surface that the mouse is resting upon, and generating a reflected image of the illuminated small area that is sensed and recorded by the electronic chip. The optical navigation sensor apparatus typically also includes one or more lenses or light pipes, for conducting and focusing the light from the LED on the small area of the surface, and for receiving the reflected image and focusing it on the electronic chip. The optical sensor navigation apparatus typically further includes an aperture plate that allows the reflected image to pass through the aperture and impinge on the electronic chip, while blocking spurious light from reaching the electronic chip.
As shown in FIGS. 1 and 2, in a typical prior optical navigation sensor apparatus 10, the electronic chip 12 and the aperture plate 14 are attached to a sensor housing 16, to form an optical navigation sensor 18. The aperture plate 14 includes an aperture, in the form of a hole 20, extending through the aperture plate 14. The sensor 18 is attached with a clip 22 to an electrical circuit board 24 mounted on a base plate 26 of an optical computer mouse 28. An LED 30 is also mounted on the circuit board 24, and a lens/light pipe 32 is positioned between the sensor 18, LED 30, and base plate 26, to direct light from the LED 30, through a hole 34 in the base plate 26, onto a small area of the surface 36 that the mouse 28 is resting upon, and to direct a reflected image of the small area of the surface 36 through the hole 20 in the aperture plate 14 to the electronic chip 12.
In order to protect the electronic chip 12 from exposure to foreign matter that could damage the chip 12, and to prevent dust particles that could interfere with operation of the chip 12 from entering the sensor 18 through the hole 20 in the aperture plate 14, a small piece of Kapton® tape 38 is glued over the hole 20. This piece of tape 38 must be removed at a proper point during assembly of the mouse 28, for the optical navigation sensor apparatus 10 to operate correctly. It is desirable that the piece of tape 38 remain in place until all soldering operations required to join the sensor 18 and LED 30 to the circuit board 24 have been completed, to prevent vapors and contamination generated in the soldering process from entering the sensor 18.
When the tape 38 is removed, it is necessary that the lens/light pipe 32 immediately be joined to the sensor 18, so that the lens/light pipe 32 can cover the hole 20 in the aperture plate 14 and prevent floating dust from entering the sensor 18. Dust in the sensor 18 can cause intermittent failures of the sensor 18, as the dust moves around inside the sensor 18 and interferes with transmission of the reflected image to the electronic chip 12. Special care must also be exercised to ensure that the piece of tape 38 does not come loose during any soldering operations, and that the entire piece of tape 38 is removed, prior to joining the lens/light pipe 32 to the sensor 18.